The invention is based on a hydraulic brake booster as generally defined hereinafter. A known brake booster of this type (German Offenlegungsschrift No. 28 25 087) is additionally equipped with an integrated anti-skid brake system (ABS) such that the brake booster can perform a dual function, namely that of brake boosting as well as that of modulating pressure for the anti-skid function. For pressure modulation, a separate valve circuit is used in combination with a specialized brake booster design, in which the master cylinder of the brake booster is utilized for pressure modulation.
Systems are also known (German Offenlegungsschrift No. 32 37 959) which operate on the principle of feeding pressure directly from the pressure medium supply system.
Typically, brake boosters are embodied such that a plurality of master brake cylinder pistons, each serving separate brake circuits I, II, III, and so on, are disposed in a housing of a brake booster, usually in line one after the other; as a result, the structural length of this kind of tandem brake booster can become considerable, especially if still further components are included in an axial arrangement, such as a pedal plate actuated by the pedal tappet and having its own spring biasing means, and the like.
It is true that an advantageously short structural length can be attained in a tandem brake booster by disposing the master brake cylinder pistons that are associated with the various brake circuits parallel to one another and preferably parallel to the brake valve as well; however, in this kind of twin design, there may be the disadvantage of considerably higher expense for components and seals, especially if the master brake cylinder pistons themselves are also supported in displaceable sheaths or bushings (this will be mentioned again later herein), which makes it possible to avoid pedal drop in the event that the pressure medium supply should fail.